Separation of salts of organic acids



Patented Dec. 15, 1953 SEPARATION OF SALTS OF ORGANIC ACIDS Vaman R.Kokatnur, New York, ,Y.; Helen G.

Kokatnur, executrix of said VamanR. Kokat- .nur, deceased No Drawing.Application September 20, 1948, Serial No. 50,241

3 Claims. -(Cl. 260-97 .6)

This invention is a continuation in part of my co-pending applicationSerial No. 569,643, filed December 23, 1944, now abandoned, and relatesto the separation of fatty acid and hydroaromatic acid such as resin orrosin acid soaps in a commercially useable form from the crude wetfloating soap, a icy-product of limit paper pulp industry.

Floating soap of the sulfate pulp industry may be termed as crude kraftsoap .or crude tall oil 1 soap. It is a by-product in the treatment ofslash or southern pine, spruce, etc, by the sulfate process to producewood-pulp. The composition of this soap comprises essentially sodiumsalts, of resinor rosin acids, i. -e., mainly abietic acid, and of fattyacids, such asoleia'linoleic, linolenic, ricinoleic acids. inexceptional cases, very small amounts of saturated fatty ;acid salts maybe present. The black liquor when separated after cooking the wood frompulp, chips, etc. and allowed to stand, yields what is known as floatingsoap as a scum on the top. This is due to salting out of the soap by theexcess sodium ions in the black liquor a phenomenon analogous to thesalting out step in soap manufacture.

The floating soap is of value not only because of the high content-ofhigher fattyacid salts but because of sodium abietate orresinate whichis valuable sizing material for paper. The fatty acid soap whenseparated as relativelypur-e soap is a valuable detergent and ifseparated in the form of free acids and then esterified produces a gooddryingoil useful in the-paint andvarnish industry. 'The-resin-or rosinacids alsohave dry ing characteristics, although not useable in thisform, 'but produce when esterified a valuable resinknown inthe trade asester gum. The soap or acid in the crude :form is a relatively valuelessmixture thathas found no utility in commerce.

Many prior attempts have been made to separate the acid constituents oftall oil which is nothing more than a mixture of all the total acidsinthe crude floating soap. Although the art is very extensive, there :isbut little information regarding the-separation of crude soapitself-into commercially useable relatively pure soaps .of fattyaci'dsrarrd resin or rosin acids. The prior art is replete with methodsof separating the acids by high vacuum distillation, differentialseparati'on'by esterificationof one type of the constituents orseparation by selective solvent action on the mixed acids. Sofar-as'lknow 'no one has successfully solved the problem ofseparating-the-two' types of soaps, via'fatty acid soaps andresin acidsoaps, from the crude kraft ,floating soap, or .a rosin soap iroma fattyacid.

I have discovered that the .two main types of soaps, .viz, fatty acidsoaps and resin .acidsoaps, can be easily, .efiiciently and economicallyseparated, and of a quality directly useable as .detergents and sizingcompositions.

It has been considered heretofore that the two types of soaps in thecrude floating soap have the same or equal solubilities in solvents andcannot be separated from each other .by selective solvent action withouttedious plurality .of operations that are ,uneconomical.

I have now discovered that certain fketones .in the presence of acritical proportionof dissolved Water, bri g about the s pa atio o ta bya id soaps by selectivesolventaction 0n the resin or sin a i soaps.Thedissolvedsoaps of resin can be separat d from the .undissolved fattya id s ps y m r ration and wash n .at -room temperature. The resin or rosin.acid soaps can be isolated by ,merely removing the solvent byevaporating or distillation.

The resin acid soapis more sensitive .to oxidation than the fatty acidsoap although both contain constituents that are subject .to oxidationeven at atmospheric temperatures when exposed to air. The oxidation, ofcourse, is enhanced at .higher temperatures .and ,is directlyproportional to its increase. The crude wet soap as originally obtainedcontains no oxidized ingredients inasmuch as the soap is normallyassociated during wood cooking with NazS, a reducing agent. Further, nomanufacturer has .re-

3 ported the presence of any .oxidized substances in such soap.

Linoleic, linolenic and resin acids .are drying acids, that ,is, theyabsorb oxygen .and polymerize forming high molecular weight, relativelyinsoluble solid compounds. When a drying oil such as linseed, tung ordehydrated castor oil dries by absorption of oxygen in the presence ofdriers .a solid, relatively insoluble film is produced. When completelyoxidized, it increases in weight by about ten percent for everydoublebond of the unsaturated acidprovided that .there are about twodouble-bonds to each acid molecule.

Drying oils on the average .contain not more than two double-bonds toeach monobasic .molecule or about six to a natural oil molecule, whichis a glyceride and hence tri-basic. The wellknown linseed oil containson the avera e two double-bonds per monobasic molecule. No natural oilis known that has a materially higher Experiments show that floating ortall oil soap when dried by exposure to air increases in weight by sixto twelve percent and if spray dried, between twelve to eighteenpercent, and is converted to a composition which is radically differentfrom that of the original in solubility, odour, color, melting point andother physical and chemical properties. It is an interesting fact thatthis weight increase is particularly noticeable in the resin or rosinsoap and negligible in the fatty acid soap. If, however, the soapcontains any traces of cobalt or manganese salts, both soaps increase inweight. The increase of weight during drying in contact with airapparently depends upon the contact surface of the soap during drying,temperature, composition of the crude soap particularly with respect toresin or rosin acid content and lastly the presence or absence of metalimpurities that may be considered as dryers or siccatives. For thesereasons, I dry the crude wet soap preferably either in contact with somevolatile solvent or in the presence of an inert gas such as nitrogen orcarbon dioxide or in the absence of air, i. e., vacuum.

The suitable solvents that may be used for drying or dewatering thecrude soap, are ketones containing not more than six carbon atoms,ethers such as isopropyl ether, methyl Cellosolve, dioxane, etc., butnot alcohols, particularly monohydric alcohols, as both the soaps areconsiderebly soluble in them. In my invention, drying the soap is not anessential part or step of the process. Inasmuch as by mixing the wetsoap with a relatively dry solvent in such an amount that by taking upand dissolving the water of the soap it becomes a selective solvent ,1

of the resin or rosin soap, a separate step of drying is not essential,and efiicient separation can be efiected by the mixing and filterin themixture. The soap on the filter is a relatively pure unoxidized fattyacid soap and the soap dis- 6 solved in the filtrate is a relativelypure unoxidized resin or rosin acid soap. Both can be used in theindustry directly without any further purification.

The ketone used for separating the two soap types may be any ketonecontaining not more than six carbon atoms to the molecule such as analiphatic ketone and containing dissolved water in the proportion of topercent of the ketone. Particularly satisfactor results are obtainedwhen the proportion of water is between 5 8 percent of the ketone. Thepercent expressed is percent by weight. If the percentage of water islower than the minimum range, the fatty acid soap separation will not beas free as the resin soap. On the other hand the higher percentage ofwater in the ketone will introduce more fatty acid soap in the separatedresin soap. To obtain the optimum separation, the percentage of water inthe ketone should be between '7 and 8 percent.

Typical ketones that illustrate the class that may be used are acetone,methyl ethyl ketone, diethyl ketone, and methyl propyl ketone. In casethe ketone selected does not have such solvent power for water todissolve the required iii percentage, then the solvent power of the saidketone may be increased by incorporating sunlcient acetone with it. Thusthe selected ketone, if not itself acetone, may contain 10 to 40 percentacetone, the higher the ketone the larger the proportion of acetonerequired within the range stated.

Example 1 One hundred parts of the floating soap containing about 35percent water, are thoroughly mixed with 250 parts of anhydrous acetoneat room temperature and the resulting mixture filtered in order toremove substantially most or the water and dry the crude soap out ofcontact with air. The resultant dry soap on the filter is then washedwith several portions of acetone containing 8 percent of water andtotaling about 500 parts. After the washing is completed, the filtercake is then removed, dried to remove the adhering acetone at lowtemperature and weighed. This was 38 parts, and had a molecular weightof 305 (304 being the theoretical for pure sodium oleate) showing therelatively high purity of the soap.

To the filtrate which contained all of the sodium salts of resin orrosin acids, acetone and water, was added an excess of toluol or benzoland the mixture evaporated to dryness by distillation. By this methodboth acetone and water are removed by partial pressure, i. e., lowtemperature, distillation and the soap after removing the hydrocarbonsolvent is found to be substantially anhydrous. The anhydrous materialwas resin soap suitable for sizing purposes and weighed 30 parts. Itsaverage molecular weight corrresponded closely to that of the sodiumsalts of the mixed acids of commercial rosin.

Example 2 One hundred parts of floating soap containing about 30 percentwater was mixed with 500 parts of anhydrous acetone and agitatedthoroughly so that the water in the soap is well dissolved in acetone.This makes the water content of acetone about 6 percent. The mixture isfiltered and washed with 94 percent acetone and the filter cake driedand weighed. The weight was 40.4 parts. Its average molecular weight was307 and the presence of a small amount or high molecular weight sodiumresinate was detected. The acetone filtrate was evaporated by partialpressure distillation at a temperature between about to 110 F., usuallyand preferably below F. in vacuum or inert atmosphere. The resulting drysodium resinate or abietate which was 32 parts, had the averagemolecular weight of sodium salts of mixed commercial rosin acids. Thesodium resinate contained traces of fatty acid soap but was just as gooda sizing material as in Example 1. The sodium soap, however, appeared tohave better detergent properties than the product of Exam- Dle 1.

Example 3 One hundred parts of floating soap reported to contain about35 percent water was first first dried by washing with 550 parts ofanhydrous acetone divided into several portions. The wet cake of 100gms. Was dried in a vacuum desiccator until it had a constant weight.This was 71 gms. showing that the reported water content given by themanufacturer was a little too high. This soap was of cream or brownishyellow color in contrast with air dried soap which is dark brown incolor and has a fishy odour.

Hist rians-t, his;r eans ass ii i tsla qm shn automatedrsiasanta tra riaSQ tt mpmdemdw Thsz aeuu sat ad tiedrsample hich-weistledflos te neiho t r 90 the filte edr.

ood; ete nts r pe issi ts reras el lar weight was.;3 o5, as in;E'xample1 and was a; relatively pure fatty acid soap. The filtratewhen-freed-from acetone and water and dried out Qrpont mw tb aiawasioundto e., .Q.- 5 s. a s and had an average molecular weight of 358 assoap, or 336 as rosin acid.- It was-quite satisfactory as a sizingmaterial.

Example 4 i one u dred arts of weti raftso ertain-v ing 35 percent wateras reported by the manufacturer, but actually percent as shown inExample 3 and the same source material, was spread out on a watch glassand dried in an oven in a current of nitrogen gas at 105 C. until itlost no further weight. The dry weight so obtained was 70.3 parts andchecked with that in Example 3, within experimental errors. This wasthen triturated with 93 percent acetone as in Example 3, and washed andfiltered and dried. The filter cake on dry basis weighed 38.6 grams andthe filtrate after freeing from acetone and water weighed 30.6 grams. Inquality both soaps were substantially as good as in Example 3.

In a modification of the invention, the higher fatty acids in thefloating soap are dis-placed by abietic acid before the sodium abietateis separated.

In this modification, there is first made a mixture including thefloating soap in substantially dry condition, added abietic acid orrosin in amount approximately equivalent to the higher fatty acidspresent in the floating soap, and an anhydrous volatile ketone. Themixture is then warmed suitably by boiling the mixture under a refluxcondenser, until the mixture which originally contained much undissolvedmaterial becomes a practically clear solution. The solution is thencooled approximately to room temperature or lower, whereupon sodiumabietate is deposited in solid form. There is left in solution freefatty acids corresponding to the major part of the fatty acidsoriginally combined with sodium in th floating soap.

As the ketone to be used in this modified method, there is used onecontaining about 6 carbon atoms to the molecule, say 4 to 8 carbonatoms, suitable materials being methyl butyl ketone, methyl isopropylketone, dipropyl ketone and ethyl propyl ketone. The ketone used shouldbe substantially anhydrous and should be a good solvent for higher fattyacids in the free condition but a poor solvent or substantially anon-solvent for sodium abietate at room temperatures.

An example of this displacement method of separating the fatty acids offloating soap is the following:

Floating soap is dewatered as by thorough washing with substantiallyanhydrous acetone, or, the soap is dewatered by forming a mixture of thewet floating soap with toluene, xylene, or like hydrocarbon liquid,distilling the mixture so that the said liquid on distillation removeswater, condensing the distilled vapors, separating the condensate intotwo layers, returning the hydrorth shedr thr e ralp r 0 racei e:

6'" rban' iquid oe hessti g QIl iimli l r heP &?-- nr 'Iltil' 1! ?iracticed nhy us assi e he110atina Qap.-suspe ed ir ue h dro ar en iqu dt t hu rdriedsoa lflw h tem eram nt; melting rr-swamps ithe-sc n,

Of. he ewater: e

om b iana sisiq he fleeti ap s se snari n ahrdr sme hy hut llte r tben aded m their- 1a refluxed-f ra es lf; ho s. In: eneral; 9;: o; .1 arts;will; suffice.) Originally the mixture contains much undissolvedmaterial but a chemical change ocours as th refluxing is continued thatmakes the solids present dissolve substantially completely. This changeis the replacement of higher fatty acids of the floating soap by abieticacid, to give additional sodium abietate. After the solution iseffected, it is cooled to approximately room temperature or lower ifdesired, during which cooling sodium abietate separates in solid form.There is thus obtained a satisfactory yield of sodium abietate. Thehigher fatty acids in free condition are left in solution.

The mixture is then subjected to processing to separate the solid sodiumabietate from the solution of the higher fatty acids; as by centrifugalseparation or by filtration. In any case, the separated sodium abietateis washed, say in the centrifuge basket or on the filter, with freshmethyl butyl ketone. The residue after washing is then warmed. toevaporate the adhering ketone, as, for example, to about 60 to C. Thesodium abietate so recovered is suitable for use in paper sizing.

The fatty acids that remain in solution are recovered by evaporation ofthe volatile ketone and used in the manufacture of soap or for otherpurposes requiring fatty acids as raw material.

It will be understood that certain details given are for the purpose ofillustration, not restriction of the invention, and that variationswithin the spirit of the invention are intended to be included withinthe scope of the appended claims.

I claim:

1. In a method of separating a crude wet soap mixture of high molecularweight of the hydro aromatic resin acid and unsaturated fatty acid asoccurring in the kraft pulp industry the steps of drying the crude wetsoap mixture under nonoxidizing conditions by washing the crude wet soapwith an aliphatic ketone having not more than eight carbon atoms, addingthereto abietic acid in amount substantially equivalent to the saidfatty acids present, warming the mixture whereby a solution results andthe abietic acid replaces fatty acids from the said salts, cooling themixture, and separating the resulting precipitate of sodium abietatefrom the remaining solution of fatty acids in the ketone.

2. In a method of separating a crude wet soap mixture of high molecularweight of the hydroaromatic and unsaturated fatty acid type occurring asthe crude wet floating soap mixture of the kraft pulp industry the stepof first drying the crude soap by washing the same under nonoxidizingconditions with a substantially anhydrous aliphatic ketone of not morethan about 8 carbon atoms having a substantial Water absorption capacityand low solubility for the soap and then separating the dry soaps fromeach other by adding to the dry soap mixture a hydrous ketone selectedfrom the group consisting of acetone, methyl ethyl ketone, di-ethylketone, methyl propyl ketone and mixtures of acetone and one of saidhigher ketones, blended with 5 to 10% of Water in which the resin soapis preferentially soluble and then separating the dissolved soapsolution from the insoluble soap residue.

3. In a method of separating a crude Wet soap mixture of high molecularweight of the hydroaromatic and unsaturated fatty acid type occurring asthe crude Wet floating soap of the kraft pulp industry, the steps offirst drying the soap by adding to the soap a volatile aromatichydrocarbon and azeotropically distilling to re- VAMAN R. KOKATNUR.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,193,785 Thurman Mar. 12, 1940 2,223,850 Gayer Dec. 3, 19402,395,282 Lovas et a1. Feb. 19, 1946

1. IN A METHOD OF SEPARATING A CRUDE WET SOAP MIXTURE OF HIGH MOLECULARWEIGHT OF THE HYDRO AROMATIC RESIN ACID AND UNSATURATED FATTY ACID ASOCCURRING IN THE KRAFT PULP INDUSTRY THE STEPS OF DRYING THE CRUDE WETSOAP MIXTURE UNDER NONOXIDIZING CONDITIONS BY WASHING THE CRUDE WET SOAPWITH AN ALIPHATIC KETONE HAVING NOT MORE THAN EIGHT CARBON ATOMS, ADDINGTHERETO ABIETIC ACID IN AMOUNT SUBSTANTIALLY EQUIVALENT TO THE SAIDFATTY ACID PRESENT, WARMING THE MIXTURE WHEREBY A SOLUTION RESULTS ANDTHE ABIETIC ACID REPLACES FATTY ACIDS FROM THE SAID SALTS, COOLING THEMIXTURE, AND SEPARATING THE RESULTING PRECIPITATE OF SODIUM ABIETATEFROM THE REMAINING SOLUTION OF FATTY ACIDS IN THE KETONE.